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As New Zealand's top players continue to adjust to the new laws around high tackling, there remains a nervousness about the All Blacks' series against the British Lions being swung by a red card.

That nervousness may sit more heavily with the All Blacks than the Lions.

Players from the Northern Hemisphere have had more playing time under the stricter laws where any tackle above the shoulders - intentional or not - is penalised.

But more pertinently, collision points have been higher in the Southern Hemisphere for longer. Super Rugby has long accepted the upper chest as a legitimate area for tacklers to target and that desire to be high impact on defence is an ingrained within the Pacific region.

The unfortunate consequence of a tackler riding up to the head after the initial contact has been made is viewed in this part of the world as a fair, occasional by-product of such aggressive defence.

The fear about red cards deciding the series is not based on any sense that one or both teams are reckless or malicious.

It is the reality of the current rules which have lowered the red card threshold - making it entirely possible that collisions which have been considered run of the mill for an age, are now deemed extreme.

The early rounds of Super Rugby have shown the difficulties players are having in adjusting. That there has only been three red cards for high tackles so far, may not suggest it has been problematic getting players to change defensive habit, but that number is 300 per cent higher than the corresponding period last year.

Every week since the competition kicked off in February there have been a significant number of tackles that challenge the officials under the current rulings.

The head is still frequently being hit in the tackle. Players from all nations are still, regularly, thrusting out their arms when they are beaten by an astute angle. Steven Luatua's high tackle on Tim Nanai-Williams in round two being remains the most obvious example of poor decision-making.

Who hasn't thought about what might happen in the test series when the pace is frenetic, the intensity off the charts and the pressure enormous?

The potential for a tackle to be mis-timed or mis-judged is major and one, unintentional mistake, could determine the outcome of a test.

Think back to the All Blacks second test against Ireland last year when both sides relentlessly went at one another. A different referee may have red carded not yellow carded Malakai Fekitoa midway through the second half for his high tackle on Simon Zebo.

There were plenty of other collisions - from both teams - that weren't intentional, but were high and the reality of test football is that the speed and agility of the attackers is such, that defenders will inevitably make mistakes.

That game showed that when the commitment of the players is total, there will be collisions that will need to be punished under the current edict around any contact to the head being sanctionable.

"Rugby is a shifting game, when you've got ball carriers that move as well as the Irish do, they're going to change direction so people are going to sometimes make mistakes, and sometimes people fall into tackles too," All Blacks coach Steve Hansen said after that test.The focus under the new laws has fallen largely on high tackles, but that game in Dublin, and the early rounds of Super Rugby have shown that players being hauled out of rucks by their necks is an equally big danger.

Neck rolling is often harder for officials to pick up which is perhaps, why, it continues to happen way more regularly than it should.

It also continues to happen because it is an effective, if illegal way, of moving bodies in dominant positions.

Blues lock Patrick Tuipulotu, who knows plenty about the collision area around the tackles ball area, says that neck rolling is sometimes the bigger worry for players in his position.

"It is an easy way to clean someone out but it is also dangerous," he says. "If you are in a strong position over the ball, no one is going to move you. The only way they are going to do that is to grab the neck.

"If you see someone over the ball like that, in that strong position, I just want to drive my shoulder through. If that doesn't work it is because they are too stong or too low over the ball.

"You might want to neck roll, but you have to make a split second decision. As a support player you want to clean the opposition out as quickly as possible and if you are coming straight on, if he doesn't move with that first shoulder contact, the next thing you have to do is hook your arm under and try to pull him away."